Amid the crush of people on the sidewalk, they waited for a guide Chun had hired to lead them to Thailand. Martial anthems blared from loudspeakers, and soldiers regularly marched past. The minutes crawled. The exhausted group huddled near a pillar, wide-eyed at the commotion around them. Sensing that if the five North Koreans stood outside much longer, an official would come up to question them, I invited them to wait in my hotel room.

For the next few hours the North Koreans sat on a long sofa, avidly watching movies on the TV. "He's so handsome," one cooed about Tom Cruise, whom she'd never heard of. They savored Cokes from the minibar and shared the fruit. "I can't even imagine what will happen next," White said, switching the channel. "I just want to get to South Korea; it seems so civilized and wealthy." She would fit in, at least on the surface. She had changed into tight jeans (illegal in North Korea), high black boots, and a frilly blouse, topped off with a heart-shaped pendant around her neck. Red switched into flashier clothes too, but she appeared lost, wrapping her arms around herself as if to squeeze out fearful thoughts. She startled when asked about her plans. "Maybe learn English, take computer classes," she said hastily. No one was thinking that far ahead.

Finally the guide called. The five grabbed their packs and hurried out. Seconds later there was a knock on the door. It was White. Laughing, she handed back the TV remote.

In his loose plaid shirt and khaki pants, Pastor Chun could have been any tourist watching the morning light glaze the brown surface of the Mekong River. Behind him a Thai town woke with a buzz of motorcycle traffic and the call of vendors selling coconuts and fish. Across the river, in Laos, a few figures stirred near stilt houses poking up out of the dense weave of forest. Chun had flown into Bangkok from Seoul the night before and had come to the Mekong shore to meet White, Red, and the other defectors. But his charges were marooned in China, and all he could do now was look across the broad river and pray.

After picking them up at the Kunming hotel, Chun's guide had driven the group over mountain roads to a safe house near the Laos frontier. And there they sat, days later, fidgeting. The guide had learned that Laos had tightened border patrols in advance of a national holiday, and he decided it was too dicey to proceed. Like their Chinese counterparts, Laotian police and military are ordered to seize escaping North Koreans and deport them. While the group waited, Black caught up with them, jittery from his clandestine train trip across China. "I almost got caught," he told them. "When police came to check documents, I pretended I was drunk, ready to pass out, and they left me alone."

News of the delay worried Chun. "They've reached the riskiest part of the journey, having to cross the Chinese border on foot and then traveling through Laos," he said as we stood by the Mekong. "They probably have a 50 percent chance of making it to here."

Chun's calling as a Good Samaritan came at age 40, when the former hotel manager surprised friends and family by joining a seminary. His activism was kindled in 1995 when, as a missionary in the Yanji region, he met his first North Koreans in hiding. "These people had lost all their rights," he said. "The most important thing I could do was revive their humanity." Given the risks, Chun has an impressive record: He has orchestrated the escapes of more than 700 North Koreans, with only a handful of failures. "The North Korean government wants me dead," he said.

But the pastor, now in his 50s and beginning to gray, is no storybook saint. His missionary contacts in China sometimes chafe at what they consider his bossy, reckless decisions; his top guide is a former drug smuggler; and Chun is not above resenting what he sees as ingratitude. "Do you know that of all the people I've helped rescue, only 30 or so have ever called to thank me," he said. But, he added, "they're not bad people. They just can't understand that someone would help them without a reward."

After nearly three weeks at the safe house, the defectors received orders to move. Shouldering packs, they entered the backcountry led by the erstwhile drug runner. The overnight hike took them into the Golden Triangle, the lawless opium-growing territory where the borders of China, Myanmar, Laos, and Thailand meet. For 16 hours they slogged in the dark through tangled forest and leech-infested streams, terrain their guide knew by heart. Climbing to nearly 4,000 feet, they stumbled out of China into Laos. "We were wet and dirty," Red said. "The ground was steep, and I kept falling. I cried most of the time."

The next afternoon the group reached a house owned by a friend of the guide. Late the next night they were driven to a spot near the Mekong, and from there they hiked to the river, lined with lookout towers. For Red, the combination of darkness, the river's strong current, and the nearby presence of Laotian soldiers made the five-minute crossing to Thailand in a small motor launch more unnerving than even the train trip across China. "I was suddenly scared of being caught; after all we'd been through, there was no guarantee we'd make it."

A Durihana pickup truck found them on the Thai side. It took them to a bus station, and ten hours later the group reached a Durihana shelter in Bangkok. There they ate their best meal in weeks and used cell phones to call friends in China to tell them they were safe. "Our prayers have been answered," Black cried out. The next morning a missionary drove the defectors to the South Korean diplomatic mission, where they requested asylum.

And then they entered a new limbo. After their names were added to a long waiting list, they were bused to an immigration detention center, where they would be warehoused for months, until South Korean officials processed their paperwork.

Defectors entered the packed detention center as fast as they were released to South Korea—30 to 40 a week while the trio was there. In the women's section of the detention center, 450 people were crammed inside a space built for half that many. "There was no room to sit or sleep. Only two toilets worked, and the air was horrible," White said. When people left, they sold their precious space, getting $400 for roughly two square feet. People who couldn't afford to pay ended up standing against a wall during the day and sleeping at night inside the toilet stalls. With help from Durihana, White and Red each bought three square feet. The men's side was also squalid, but less crowded. (Since then conditions have improved, as the South Korean government has sped up its admissions process, thinning out the crowd.)

After nearly 80 days of confinement in Thailand, Red, White, and Black were told to gather their meager belongings for the last leg of their journey. A plane was waiting.

Nothing prepares North Koreans for the impact of Seoul. For Red, the moment of arrival was overwhelming. "I kept touching my face, thinking, Is this real, is this a dream?" she said, recalling the sensation of watching buildings and streets bloom beneath her as she landed at Incheon International Airport. Then came the bus ride along the Han River past downtown Seoul, the embodiment of the South's hypercompetitive, prosperous, fast-paced life, a world more complex and foreign than any the refugees had encountered. What little the defectors know of the South is distorted by North Korean propaganda—the South is enemy territory, the land of murdering capitalists—or by images from soap operas and movies smuggled into the North, or by fantasies that success will come fast and easy in the southern paradise. A North Korean who had been living in Seoul for two years summed up the culture shock: "The difference between North and South is like jumping ahead a century."

After being debriefed to make sure they're not spies, defectors are sent to Hanawon, a high-security facility south of Seoul, where for two months they receive mandatory instruction in South Korean culture and practical matters such as taking the subway and opening a bank account. They're granted South Korean citizenship, paid a settlement bonus of roughly $5,000, with small monthly installments to follow, and provided a housing allowance and employment incentives.

In the mid-1990s the few dozen defectors arriving each year were greeted with adulation and hefty rewards; most were elite members of the military or Communist Party from Pyongyang who brought valuable intelligence. With rare exceptions, today's defectors, averaging more than 2,000 a year since 2006, are farm laborers, factory workers, and low-level soldiers and clerks from impoverished regions. What they bring mostly are problems. Compared with the average South Korean, they are markedly less educated and skilled. Having experienced years of malnutrition and the pain of seeing family members die of starvation, many suffer from serious physical and mental illnesses. Because of these handicaps, says Andrei Lankov, a North Korean expert at Kookmin University in Seoul, the defector population is in danger of "becoming a permanent underclass." Their life in the South is immeasurably richer and freer, but they crave a sense of belonging. "Most South Koreans are indifferent to their plight," Lankov said. "And to not have your suffering recognized is an almost unbearable form of violence."

Red answered at the first knock, throwing open the door of her 12th-floor apartment in Incheon, near the airport. Eight months had passed since I'd seen her hurry from a hotel room in China, a scared, dark-eyed teenager on the run. Her face was rounder now, her arms fleshier, thanks to regular meals. She'd streaked her hair red and was dressed in black jeans and a T-shirt. Proudly, she showed me her home of seven weeks, a spotless two-room apartment, bare except for a mattress on the bedroom floor and a desk crowned with a personal computer. A sheet of paper taped to a wall showed pink Chinese characters for happiness.

"Kimchi!" she squealed, using the Korean equivalent of "Say cheese!" as she shot pictures and video with her new camera. Deft as any South Korean youth, she downloaded the images and zapped them to my wife in the U.S.

Red showered bars of chocolate on my lap and ordered me to eat. I suspected that I was a rare guest. "Do you have many friends?" I asked. She shook her head vehemently. "How can I make friends if I can't make sense of the society outside?" She confessed that she rarely left the apartment, self-conscious about her accent and not understanding the language South Koreans use, with its liberal sprinkling of English words. Red also didn't feel confident about her job prospects. Language courses and classes in hairstyling cost too much for her monthly $400 government check, and with only a high school education, she was probably limited to low-wage jobs. She had already quit a job at a gas station and now was thinking about working in a cafeteria. "At job interviews," she said, "I'm afraid to say I'm North Korean, because of all the disadvantages that come with it."

We ate fish and rice at a nearby restaurant, where Red snapped more pictures, giggled, sent messages to fellow defectors on her cell phone, and practiced saying "computer" in English. "Life is tough here, but I'm glad I came," she said, before returning to her sanctuary. "I still dream of being a success. I want to make my parents in North Korea proud of me."

White was sharing a hospital room with five other women in the provincial city of Cheonan, near the Hanawon resettlement facility. At Hanawon doctors had diagnosed her with thyroid cancer, and they immediately operated. If she had remained in North Korea, or even in China, she almost certainly would have died. Now she had a chance of healing.

She rose unsteadily from her hospital bed to greet me, a shy smile on her face. A scar from the surgery extended around to the base of her throat. The intense young woman I remembered, with the deep laugh and showy clothes, now teetered in baggy pajamas, her voice a hoarse whisper. "I called Pastor Chun to thank him," she said. "Durihana is helping pay for my treatment. Sometimes Pastor Chun comes here, and we pray together." White, Chun had told me, is a committed Christian—"the real thing, a good, pure spirit."

White had already visited the apartment she hoped to move into. "First I will buy a computer and a refrigerator," she said, "and I will cook North Korean dishes." She caught me staring. I couldn't help it. She had spent a year locked in a room in China, followed by three months in a crowded detention center in Thailand, and now three months in a hospital room, during which time she had learned of her mother's death and her brother's imprisonment. How could she look so beatific? She walked outside with me to the taxi stand to say goodbye, and when I looked back from the car, White was still standing there, smiling at the spacious sky.

Black moved into an apartment in downtown Seoul, not far from the Han River. Traffic noises and the hum of cicadas drifted through his windows. On a wall hung the wooden cross he'd held so tightly in China, and a Bible lay open on the floor amid other books. He hadn't bought any furniture yet. "Everything is more difficult and complicated than I was prepared for," the 40-year-old said. His dream of attending seminary was dashed when he learned that scholarships were restricted to those under 35. For now he was a day laborer at a construction site. "I need to make money fast to bring my brother and sister out of North Korea," he said.

Whenever he heard himself complaining to me, Black apologized. "I am so relieved to be here. When I read about street demonstrations in Seoul, I get so happy. If I did that in North Korea, I would be sent to prison."

We hailed a taxi to take us across town to a student neighborhood filled with cheap, noisy restaurants. Horns shouted, and signs and pedestrians swept past in a blur. Eight months earlier, in a missionary's van in China, Black's shoulders had been hunched, his eyes alert to danger, his hand clutching his cross. Now amid the glorious tumult of his new home, Black closed his eyes and dozed off. He was safe, and he was free.

Tom O'Neill is a senior writer for the Geographic. Taiwan native Chien-Chi Chang is with the Magnum photo agency and lives in Taipei and New York City.